Just tell her you like her. After all you can't read her body language therefore the only option you really have is the direct approach.

If you think there's a danger it could ruin your friendship or if you can foresee fundamental difficulties in a potential relationship with her then that's a call you have to make.

Therefore in my opinion you have two options
-be direct about your feelings with her.
-resign yourself to the fact that she's unattainable based on the circumstances/risks and just enjoy your friendship with her for what it is.